This invention is an improvement in heatseal dies used to form a heatseal between two heatsealable surfaces. Such dies are employed in packaging machines to form the top and bottom seals of packages made from thermoplastic film. The typical seal seen on such packages has vertical serrations. The vertical serrations provide a strong seal, but not a good airtight seal. Packages which are not airtight are called leakers. U.S. Pat No. 4,001,075 describes an improved heatseal die for avoiding leakers. The die has longitudinal (horizontal), truncated lands that substantially conform to corresponding grooves. The depth of each groove is substantially equal to the height of the corresponding land. As a result, the top of each land contacts the bottom of the corresponding groove. In the die of this invention the height of the land is less than the depth of the groove. As a result, the top of the land does not contact the bottom of the groove, and therefore more shear is imparted to the heatsealable surfaces, which produces a better airtight heatseal.